In the book of the prophet Isaiah, we find the Expression "God of Truth" (literally "God of the Amen"), that is, the God who is Faithful to his Promises: "He who blesses himself in the land shall bless himself by the God of truth [amen]." 645 Our Lord Often used the word "Amen," sometimes repeated, 646 to emphasize the Trustworthiness of his teaching, his Authority founded on God's truth.